The present invention relates to a cooling apparatus for circulating a cooled brine used for a freezing show case, a refrigerating show case, a freezer, a refrigerator and the like.
Conventionally, a freon refrigerant has been used as a refrigerant employed in a compression type refrigerating machine, however, by reconsidering an ozone layer breakage and an earth warming-up, it has been considered in a cooling apparatus to employ ammonia as a refrigerant. A flooded type cooling apparatus or a liquid circulating type cooling apparatus are described, for example, in Japanese Patent Unexamined Publication No. 10-170124 as a cooling apparatus employed in an ammonia freezer.
Further, in order to reduce an amount of the refrigerant sealed within a refrigerating cycle, it has been known to be proper to use a plate type heat exchanger represented by a herringbone plate, a corrugate plate and the like in an evaporator.
Since a large amount of refrigerant is required in the flooded type and liquid circulating type cooling apparatuses in accordance with the prior art, they do not address the problems of the ozone layer breakage and global warming, and it is necessary to sufficiently consider an efficiency, a risk and the like in the case of employing ammonia.
Further, in the case of using the plate type heat exchanger, it is necessary to consider a risk that an internal freezing is generated when a flow rate of the brine is reduced and a heat transmitting pipe forming the heat exchanger is clogged so as to be deformed or broken.
An object of the present invention is to provide a brine cooling apparatus which can solve the problems mentioned above, prevent a brine from freezing within a heat exchanger, improve reliability and secure a stable operation.
Further, another object of the present invention is to provide a brine cooling apparatus which addresses an environmental problem by reducing an amount of used refrigerant, reducing a fear of breaking the ozone layer and preventing global warming.
Still further, another object of the present invention is to provide a brine cooling apparatus which can secure an improvement in performance with a reduced amount of a refrigerant, provide an improved efficiency even when employing a natural type refrigerant, and increase safety with respect to combustibility and a poison of the natural type refrigerant.
Here, the present invention is constituted such as to solve at least one of the problems mentioned above.
In order to achieve the objects mentioned above, in accordance with the present invention, there is provided a brine cooling apparatus including a screw compressor, a condenser, a main expansion valve, an evaporator, a pipe for connecting the screw compressor, the condenser, the main expansion valve and the evaporator, a refrigerant evaporated by the evaporator, and brine flowing through the evaporator. The brine is cooled by evaporating the refrigerant by the evaporator. The refrigerant is an ammonia refrigerant, the evaporator is a plate type heat exchanger constructed by stacking a plurality of plates, and capacity control means is provided in such a manner as to control a capacity of the screw compressor in accordance with the flow rate of the brine.
Since ammonia is employed as the refrigerant, there is no risk of breaking the ozone layer and warming the earth, and an amount of the used refrigerant can be reduced to serve as an evaporator. The plate type heat exchanger is structured by stacking a plurality of plates. Then, since the capacity of the screw compressor which can obtain a high output is controlled in accordance with the flow rate of the brine, freezing within the heat exchanger caused by reducing the amount of the sealed refrigerant can be prevented and reliability can be improved.
Further, in accordance with the present invention, there is provided a brine cooling apparatus including a screw compressor, a condenser, a main expansion valve, an evaporator, a pipe for connecting the screw compressor, the condenser the main expansion valve and the evaporator, a refrigerant evaporated by the evaporator, and brine flowing through the evaporator, the brine being cooled by evaporating the refrigerant by the evaporator. The refrigerant is an ammonia refrigerant, the evaporator is a plate type heat exchanger constructed by stacking a plurality of plates, flow rate detecting means for detecting a flow rate of the brine is provided, and capacity control means is provided in such a manner as to reduce an operating capacity of the screw compressor in the case that the reduction of the flow rate of the brine is detected by the flow amount detecting means.
A cooling load is reduced together with a reduction of the flow rate of the brine; however, since the operating capacity of the screw compressor is reduced in the case that the reduction of the flow amount of the brine is detected, a temperature of the brine is not excessively lowered to a freezing temperature. Accordingly, it is possible to prevent freezing within the heat exchanger and improve reliability.
Still further, in accordance with the present invention, there is provided a brine cooling apparatus including a screw compressor, a condenser, a main expansion valve, an evaporator, a pipe for connecting the screw compressor, the condenser, the main expansion valve and the evaporator, a refrigerant evaporated by the evaporator, and brine flowing through the evaporator, the brine being cooled by evaporating the refrigerant by the evaporator. The refrigerant is an ammonia refrigerant, the evaporator is a plate type heat exchanger constructed by stacking a plurality of plates, and suction pressure detecting means for detecting a suction pressure of the compressor and capacity control means are provided in such a manner as to reduce an operating capacity of the screw compressor in the case that it is judged by the suction pressure detecting means that the suction pressure of the compressor is lowered.
When the flow rate of the brine is reduced, the cooling load is reduced and the suction pressure of the compressor is lowered. Then, in the case that it is judged by the suction pressure detecting means that the suction pressure of the compressor is lowered, the operating capacity of the screw compressor is reduced, so that it is possible to prevent the brine within the heat exchanger from freezing during a normal continuous operation.
Furthermore, in accordance with the present invention, there is provided a brine cooling apparatus including a screw compressor, a condenser, a main expansion valve, an evaporator, a pipe for connecting the screw compressor, the condenser, the main expansion valve and the evaporator, an ammonia refrigerant evaporated by the evaporator, and brine flowing through the evaporator, the brine being cooled by evaporating the refrigerant by the evaporator. The evaporator is a plate type heat exchanger constructed by stacking a plurality of plates, and capacity control means for controlling a capacity of the screw compressor, suction pressure detecting means for detecting a suction pressure of the compressor, and capacity control means for reducing an operating capacity of the screw compressor in the case that the suction pressure of the compressor is continued lower than or equal to a predetermined value for a fixed time are provided.
Accordingly, since the operating capacity of the screw compressor is reduced in the case that the suction pressure of the compressor is continued lower than or equal to a predetermined value for a fixed time, it is possible to securely prevent the brine within the heat exchanger from freezing during a normal continuous operation, so that the plate type heat exchanger can be used for the exchanger in order to reduce the amount of the ammonia sealed within the refrigerating cycle, and the structure can be made preferable for preventing the ozone layer breakage and the global warming.
Further, in accordance with the present invention, in the brine cooling apparatus mentioned above, it is desirable to set the predetermined value of the suction pressure to a saturated pressure corresponding to a temperature 5 to 10xc2x0 C. higher than the brine freezing temperature.
Still further, in accordance with the present invention, in the brine cooling apparatus mentioned above, it is preferable to reduce the operating capacity of the screw compressor from a 100% operating capacity to a 50% operating capacity in view of an operating efficiency and the like in the case of again returning to a cooling operation from the operation for preventing the freezing.
Furthermore, according to the present invention, in the brine cooling apparatus mentioned above, it is advantageous to employ a pressure switch as the suction pressure detecting means in view of cost reduction and reliability.